1. Field of the Invention
This invention relates to medical leads for providing electrical signals to a human organ, such as a heart, and more particularly, to an epicardial lead having a stable fixation system adapted for quick attachment without extensive operative procedures to suture or connect the lead to the heart surface.
2. Description of the Prior Art
Heart leads are used to provide an electrical connection between a pulse generator and a patient's heart. In a great majority of the cases where the pulse generator is implanted within a patient on a permanent basis, transvenous leads are used, wherein the lead is introduced into the heart through a convenient vein. This procedure avoids the requirement of having to establish direct access to the heart itself. Such leads also avoid the trauma of actually inserting the lead into the heart wall. The endocardial lead as disclosed in U.S. Pat. No. 4,506,680 to Stokes, for example, has proven very successful for use in a large majority of cases.
In a certain percentage of cases, however, it is deemed necessary or desirable to use an external or epicardial lead, wherein the electrode or electrodes are mechanically inserted into the epicardium. In this arrangement, it is necessary the insertion be made with a minimum of trauma but yet be absolutely secure so that good electrical contact is maintained with the heart. Historically, one form of such an epicardial lead has involved actually suturing the lead onto the heart wall to thereby insure the required security. This has the great disadvantage, however, of increasing the complexity of the operative procedure required to implant such a lead.
To overcome the difficulties and complexities presented by use of a sutured epicardial lead, the medical device industry has developed a screw-in epicardial lead. This lead consists of a helical coil which is screwed into the heart wall. Examples of such a lead are disclosed in U.S. Pat. No. 5,154,183 to Kreyenhagen et al., U.S. Pat. No. 5,143,090 to Dutcher et al., U.S. Pat. No. 5,085,218 to Heil Jr. et al. and U.S. Pat. No. 4,010,758 to Rockland et al. This type of lead, however, requires sufficient room to approach the heart wall from a direction more or less perpendicular to the surface to enable the helical coil to be screwed directly into the heart muscle. Even if a perpendicular approach is not required, the physician must still have sufficient access to the heart so as to be able to push and rotate the helical coil tip into the epicardium.
An alternative to a screw-in lead may be seen in U.S. Pat. No. 4,177,818 to DePedro which discloses an epicardial electrode constructed from a pliable material and having a series of fixation prongs. This lead, however, requires the use of a tool or instrument to deform the lead body back against itself in order to attach it to the heart surface. A variation on such a flexible epicardial lead is disclosed in U.S. Pat. No. 4,144,890 to Hess which shows a lead which must be flexed forward with a tool, rather than backward, against itself in order to insert it into the epicardium.
While these leads have enjoyed a reasonable success to date, they still offer many possibilities of improvement. The heart is an organ constantly undergoing movement. This motion presents at least two difficulties. First, constant motion will tend to cause an object to be expelled from the heart. The fixation mechanisms of these leads have not been shown to be wholly secure. In addition, while providing stable fixation, it is also important that the lead not damage the tissue to thereby provoke formation of scar tissue. Scar tissue affects the electrical properties of the tissue and thus may inhibit the performance of the lead. This is especially likely in cases where the lead creates a relatively large amount of scar tissue.